Magnetron tube having alternate cavities of the anode structure directly coupled to a stabilizing cavity



g- 1, 1967 E. T. DOWNING 3 334,268

MAGNETRON TUBE HAVING ALTER NATE 'CAVITIES OF THE ANODE STRUCTURE DIRECTLY COUPLED TO A STABILIZING CAVITY Filed Sept. 25, 1963 2 Sheets-Sheet 1 INVENTOR EDWARD T DOWN/N6 Aug. 1, 1967 E. T. DOWNING 3,334,268

MAGNETRON TUBE HAVING ALTERNATE CAVITIES OF THE ANODE STRUCTURE DIRECTLY COUPLED TO A STABILIZING CAVITY Filed Sept. 25, 1965 2 Sheets-Sheet 2 AGE/VT United States Patent MAGNETRON TUBE HAVING ALTERNATE CAV- ITEES OF THE ANODE STRUCTURE DIRECTLY COUPLED TO A STABILIZING CAVITY Edward T. Downing, Winchester, Mass., assignor to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Sept. 25, 1963, Ser. No. 311,490 7 Claims. (Cl. 31539.65)

This invention relates to magnetrons and more particularly to a frequency stabilized megnetron.

For proper magnetron operation it is generally necessary to maintain the frequency of the magnetron power output stable and constant under varying load conditions, operating current levels and environmental conditions. In order to achieve such frequency stability it has been the practice to couple an auxiliary resonant cavity to one or more of the magnetron resonant cavities formed by the vanes or slots of the magnetron anode structure. Stabilization is achieved by maintaining the stored energy in the combined anode-auxiliary cavity system greater than that of the anode resonant cavity structure alone. However, preservation of the angular symmetry of the Ir-mode of magnetron operation presents a problem in the coupling of an auxiliary cavity to an anode structure. The 1r-mode of operation corresponds to an RF field configuration in which the RF phase alternates 180 between ad iacent anode cavities. The frequency of the 1r-mode is approximately equal to the resonant frequency of one of the anode cavity resonators. Mutual coupling between anode cavities results in N/2 possible modes of operation in an N cavity anode structure. All modes except the vr-rnode are degenerate, that is, they can oscillate at two different frequencies. Consequently, the 1r-mode is preferred over the others. To preserve angular symmetry of the dominant mode of operation when coupling an auxiliary cavity to the anode structure it is necessary that at least each alternate anode resonant cavity be affected by the auxiliary cavity in the same manner.

Accordingly, it is an object of the present invention to provide frequency stabilized magnetrons having symmetrical coupling between the auxiliary cavity and the anode structure.

As is known, a stabilized magnetron having symmetrical coupling comprises the so-called coaxial magnetron wherein a cavity operating in the TE mode and disposed coaxial to the interaction space formed between the anode vane cavities and the cathode is coupled to the anode structure by means of slots in the rear of alternate anode vane cavities. The coaxial magnetron is structurally limited to a TE mode auxiliary cavity by virtue of its peculiar slotted vane coupling arrangement. Accordingly, flexibility in the construction and dimensions of the auxiliary cavity is severely narrowed. Furthermore, since the auxiliary cavity is coaxial to the interaction space, the diameter of the over-all structure'is greatly increased. In applications such as in airborne beacon tubes where space, size and hence weight are critical, such an increase in diameter is greatly disadvantageous. Accordingly, it is a further object of the present invention to provide a frequency stabilized magnetron including an auxiliary cavity wherein the over-all structure is relatively compact in size and of reduced complexity.

In accordance with the present invention there is provided a stabilizing cavity for a magnetron disposed longitudinally adjacent to the anode cavity structure. The stabilizing cavity is coupled to alternate anode resonant cavities by means of suitably disposed probes, loops, irises or the like. There is thus achieved a relatively compact inexpensive frequency stabilized magnetron having symmetrical coupling between the anode structure and the be limited by the use herein of the particular tuning 3,334,258 Patented Aug. 1, 1967 stabilizing cavity thereby permitting wide band frequency operation with high efliciency.

Furthermore, in many of the magnetrons presently being produced an end space exists which is defined by one of the magnetron pole pieces and the anode vane structure. This end space, not now serving a useful function, may be adapted in accordance with the present invention to form a portion of the auxiliary cavity structure, thereby resulting in a stabilized magnetron with over-all dimensions substantially identical to the conventional unstabilized magnetron. Various other objects and advantages will appear from the following description of several embodiments of the invention taken in connection with the accompanying drawings, wherein:

FIG. 1 is a vertical section of a magnetron constructed in accordance with the invention;

FIG. 2 is a cross-section through said magnetron along the line 2-2 of FIG. 1 and reduced in scale and rotated slightly to show the details of the coupling probe of the embodiment of FIG. 1;

FIG. 3 illustrates an alternate embodiment of the invention wherein loop type coupling between the auxiliary cavity and the anode cavity structure is utilized; and

FIG. 4 illustrates a further embodiment of the invention wherein iris-type coupling is utilized in connection with a beacon type magnetron having a pre-existing end space.

In the embodiment of the invention illustrated in FIGS. 1-2 the device includes a substantially cylindrical cathode 10 surrounded by a plurality of anode vanes 11 which terminate in an annular anode ring 12. A magnetic field is maintained parallel to the magnetron axis, that is, the axis of the cathode 10, in the well known manner as by permanent magnet 18. The magnetic circuit includes two magnetic pole pieces 13 and 14 coupled to the poles of magnet 18. The lower pole piece 13 is provided with a hollow core for passage of external leads, not shown, to cathode 10. The power output of the magnetron is coupled to an external load, not shown, in the well known manner by loop 30 located in one of the resonant cavities formed by the anode vane structure. Alternate anode vanes 11 are connected in the well known manner to one of two circular conducting straps 15 and 16.

The stabilizing cavity 21 of the invention is disposed adjacent the anode vane structure co-extensive therewith and displaced therefrom along the longitudinal axis A of the cathode 10. The stabilizing cavity i defined by the wall surfaces 21A, B, C and D. In the embodiment of FIGS. 1-2 symmetrical coupling of the energy between the stabilizing cavity 21 and the anode vane structure is accomplished by providing coupling means 24, comprising a probe 22 having legs 23, in electrical contact between the cavity 21 and alternate vanes Ila-11d of the anode structure. Probe 22 extends through hollow core 26, upper pole piece 14 and into cavity 21 through aperture 28 provided therein. Legs 23 electrically couple probe 22 to the alternate vanes of'the anode structure.

Frequency tuning of the magnetron is accomplished by varying the internal dimensions of auxiliary cavity 21. To this end, there is provided a screw 36 driven by a trapped nut 39 held by bearing race 38 fastened to panel member 37. Upper wall 21D of cavity 21 is flexibly attached by means of annular flexible plate 35 to panel member 37. Accordingly, as screw 36 is moved down it depresses upper wall 21D towards probe 24 in the desired fashion, thereby decreasing the interior dimensions of the cavity. Upward motion increases the interior dimensions of cavity 21. Various other devices are available for changing cavity dimensions and the invention should not mechanism above described.

Preferably resonant cavity 21 is constructed so as to operate in the TM mode as illustarted by the vector lines 33 and 34 designating the electric field vectors and the magnetic field vectors respectively. It is noted that the device will operate with modes such as the TE and TM among others, with satisfactory results. The probe type coupling illustrated in the embodiment of FIGS. 1 and 2 in connection with a TM mode cavity is essentially a capacitive type coupling system. In the embodiment now to be described an inductive type coupling configuration is shown.

In the embodiment of FIG. 3 the drawing therein has been simplified where the details are substantially the same as that of FIGS. 1 and 2. Numeral 4t) designates an anode vane structure similar to that of FIGS. 1 and 2. Alternate anode segments of the anode vane structure are connected to one of two circular conducting straps 45 and 46. In the customary manner an external cathode voltage source (not shown) is connected to cathode 41. A magnetic field is provided by means of pole pieces 43 and 44 coupled to a suitable magnet (not shown). Output power is taken from the magnetron by coupling a coaxial cable to straps 45 and 46.

, A stabilizing cavity 51 preferably operating in the TM mode is provided longitudinally adjacent cathode 41. One of the walls of the cavity is formed by pole piece 44. N 2 coupling loops 42 are provided which couple alternate vanes 40 of the N vane anode structure of the interior of the auxiliary resonant cavity 51. The letter N indicates that any even number of vanes 2, 4 N may be employed in the anode structure of FIG. 3. The coupling loops 42 are curved as shown so that electromagnetic energy within the cavity 51 will be induced therein. It is noted that to enhance the inductive process, the curved portion or loop portion of loops 42 are situated so that the plane of the loop is normal to the magnetic lines whereas in the probe coupled device of FIGS. 1 and 2 the axis of the probe is parallel to the electric lines.

In the embodiment shown in FIG. 4 an iris coupled cavity 60 of the invention is illustrated. In this embodiment the stabilizing cavity 60 is formed into the end space normally associated with beacon type ma'gnetrons having pole pieces extending into the anode vane structure. Accordingly, the over-all dimensions of the magnetron incorporating the stabilizing cavity remain unchanged as compared to a conventional unstabilized magnetron. It is also noted that either probe type coupling or loop type coupling illustrated in FIGS. 1-3 may be employed in the device illustrated in FIG. 4 as was explained in connection with the aforesaid figures.

The anode vane structure 62 of FIG. 4 will be seen to comprise a relatively H-shaped structure when viewed in cross-section. The cross-bar of the H comprises the vane cavity resonators 63 disposed about an interaction space having a cathode element 64 in the center thereof.

Magnetic pole pieces 66 and 68 extend into the interior of the H-shaped structure closing off the top and bottom of the anode vane structure. An aperture 74 is provided in pole-piece 66 to permit entry and connection of a coaxial cable to cathode element 64. A similar aperture 69 is provided in one wall of the anode structure to permit entry of a loop 70 into the interior of one of the anode vane resonant cavities thereby to provide coupling means for extracting power from the magnetron. Pole piece 68 has formed therein a cavity 60 which preferably operates in the TM mode. The top wall 60a is flexibly mounted to the cavity in the manner described in connection with FIG. 1 to permit frequency tuning of the magnetron by means of screw 72 attached to wall 60a. N 2 irises where N is the number of anode cavities are located in bottom wall 60b and disposed adjacent to and coextensive with corresponding N/2 anode vane resonant cavities to permit coupling of energy therebetween.

The location of the magnet which provides the magnetic field parallel to the longitudinal axis of the magnetron is partially shown in dotted lines.

This completes the description of the embodiments of the invention illustrated herein. However, modifications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, slot or hole type resonant cavities may be substituted for the vane type cavities disclosed. Accordingly, it is desired that the invention not be limited to the particular details of the embodiment disclosed herein except as defined by the appended claims.

What is claimed is:

1. In combination:

a cathode;

an anode structure including a plurality of vanes forming resonant cavities about said cathode;

means for producing a magnetic field parallel to the longitudinal axis of the cathode;

a stabilizing cavity displaced from said anode structure along the longitudinal axis of said cathode;

and coupling means for symmetrically coupling energy between said stabilized cavity and alternate resonant cavities of said anode structure, said coupling means comprising a probe extending into said stabilizing cavity with legs extending from said probe to alternate resonant cavities of said anode structure.

2. In combination:

a cathode;

an anode structure including a plurality of vanes forming resonant cavities about a cathode;

means for producing a magnetic field parallel to the axis of said cathode;

a stabilizing cavity displaced from said anode structure along the longitudinal axis of said cathode;

and coupling means for symmetrically coupling energy between said stabilizing cavity and alternate resonant cavities of said anode structure, said coupling means comprising a plurality of loops, each loop extending axially at one end into said stabilizing cavity and at the remaining end to an alternate resonant cavity of said anode structure.

3. In combination:

a cathode element;

an anode structure including a plurality of vanes forming resonant cavities;

means for producing a magnetic field parallel to the longitudinal axis of said cathode; a stabilizing cavity displaced from said anode structure along the longitudinal axis of said cathode;

and coupling means for symmetrically coupling energy between said stabilizing cavity and alternate resonant cavities of said anode structure, said coupling means comprising a plurality of irises, each iris dispose-d intermediate an alternate resonant cavity and said stabilizing cavity.

4. In combination:

a cathode element;

an anode structure including a plurality of vanes forming resonant cavities about said cathode;

means for producing a magnetic field parallel to the longitudinal axis of the cathode; a stabilizing cavity displaced from said anode structure along the longitudinal axis of said cathode;

coupling means for symmetrically coupling energy between said stabilized cavity and alternate resonant cavities of said anode structure, said coupling means comprising a probe extending into said stabilizing cavity with legs extending from said proble to alternate resonant cavities of said anode structure;

said magnetic field producing means including a member of a magnetic material disposed between said anode structure and said stabilizing cavity;

means for varying the internal dimensions of said stabilizing cavity;

and means for extracting energy form one of the resonant cavities of said anode structure.

5. Incombination:

a cathode element;

an anode structure including a plurality of vanes forming resonant cavities about a cathode;

means for producing a magnetic field parallel to the longitudinal axis of the cathode;

a stabilizing cavity displaced from said anode structure along the longitudinal axis of said cathode;

said magnetic field producing means including a member of magnetic material disposed between said anode structure and said stabilizing cavity;

coupling means for symmetrically coupling energy between said stabilized cavity and alternate resonant cavities of said anode structure, said coupling means directly connecting said stabilizing cavity to alternate resonant cavities of said anode structure;

means for varying the internal dimensions of said stabilizing cavity;

and means for extracting energy from one of the resonant cavities of said anode structure.

6. A magnetron comprising:

a cathod element;

an anode structure including a plurality of resonant cavities disposed about said cathode and forming an interaction space therebetween;

a TM' cavity displaced from said interaction space along the longitudinal axis of said cathode;

means for coupling energy directly between said TM cavity and alternate resonant cavities of said anode structure while preserving angular symmetry of the dominant mode of oscillation of said magnetron;

means'for extracting energy from one of said resonant cavities;

and means for providing a magnetic field parallel to the longitudinal axis of said cathode;

said magnetic field producing means including a member of magnetic material disposed between said interaction space and said TM cavity.

7. A magnetron comprising:

a cathode element;

an anode structure including a plurality of resonant cavities disposed about said cathode and forming an interaction space therebetween;

a TM cavity displaced from said interaction space along the longitudinal axis of said cathode;

means for coupling energy directly between said TM cavity and alternate resonant cavities of said anode structure while preserving angular symmetry of the dominant mode of oscillation of said magnetron;

means for extracting energy from one of said resonant cavities;

means for providing a magnetic field parallel to the longitudinal axis of said cathode;

said magnetic field producing means including a member of magnetic material disposed between said TM cavity and said anode structure;

and means for varying the internal dimensions of said TM cavity.

References Cited UNITED STATES PATENTS 2,589,903 3/1952 Vitter 31539.77 X 2,611,110 9/1952 Powers 31539.77 X 2,666,165 1/1954 Hutchinson 31539.77 X 2,769,937 11/1956 Hutchinson et al. 31539.77 2,854,603 9/1958 Collier et al. 31539.77 3,064,158 11/1962 Buck 315-39.77 X

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, JR., Assistant Examiner. 

5. IN COMBINATION: A CATHODE ELEMENT; AN ANODE STRUCTURE INCLUDING A PLURALITY OF VANES FORMING RESONANT CAVITIES ABOUT A CATHODE; MEANS FOR PRODUCING A MAGNETIC FIELD PARALLEL TO THE LONGITUDINAL AXIS OF THE CATHODE; A STABILIZING CAVITY DISPLACED FROM SAID ANODE STRUCTURE ALONG THE LONGITUDINAL AXIS OF SAID CATHODE; SAID MAGNETIC FIELD PRODUCING MEANS INCLUDING A MEMBER OF MAGNETIC MATERIAL DISPOSED BETWEEN SAID ANODE STRUCTURE AND SAID STABILIZING CAVITY; COUPLING MEANS FOR SYMMETRICALLY COUPLING ENERGY BETWEEN SAID STABILIZED CAVITY AND ALTERNATE RESONANT CAVITIES OF SAID ANODE STRUCTURE, SAID COUPLING MEANS DIRECTLY CONNECTING SAID STABILIZING CAVITY TO ALTERNATE RESONANT CAVITIES OF SAID ANODE STRUCTURE; MEANS FOR VARYING THE INTERNAL DIMENSIONS OF SAID STABILIZING CAVITY; 